1. Field of the Invention
The present invention relates to an ultrapure water producing apparatus, and more particularly to an ultrapure water producing apparatus having a replaceable unit apparatus.
2. Description of the Background Art
In an industry where ultrapure water is used such as the semiconductor industry or the medical industry, it is becoming necessary to remove impurities at the level of ppt (parts per trillion) to ppq (parts per quadrillion). For removal of impurities at this level, there are introduced unit apparatuses such as an ultraviolet oxidation unit with low pressure mercury lamp, an ion exchange resin and ultrafiltration equipment.
Since such unit apparatuses are consumable products, they need to be replaced at regular time intervals, however, elution of impurities from these unit apparatuses is detected just after the replacement. This eluted component is not acceptable for impurity control at the level of ppt to ppq. However, it is in fact extremely difficult to reduce the eluted component to zero.
A first aspect of the present invention is directed to an ultrapure water producing apparatus. The ultrapure water producing apparatus comprises: an ultraviolet oxidation unit and an ion exchanger provided in this order from the upstream side of a direction in which pure water flows; an oxidant decomposition unit for sampling pure water already undergone ion exchange in the ion exchanger, thereby decomposing all of oxidants included in sampled pure water into dissolved oxygen; and a feedback system for measuring a first dissolved oxygen concentration in the pure water already undergone ion exchange and a second dissolved oxygen concentration in pure water already decomposed in the oxidant decomposition unit to calculate a third dissolved oxygen concentration indicating a difference between the first and second oxygen concentrations, thereby adjusting the amount of ultraviolet light of the ultraviolet oxidation unit based on the third dissolved oxygen concentration.
According to a second aspect of the present invention, in the ultrapure water producing apparatus of the first aspect, the feedback system includes: a first dissolved oxygen concentration meter for detecting the first dissolved oxygen concentration; a second dissolved oxygen concentration meter for detecting the second dissolved oxygen concentration; and a control system for calculating the third dissolved oxygen concentration upon receipt of data from the first and second dissolved oxygen concentration meters and controlling the amount of ultraviolet light of the ultraviolet oxidation unit.
According to a third aspect of the present invention, in the ultrapure water producing apparatus of the first aspect, the oxidant decomposition unit includes a system for alkalizing the sampled pure water already undergone ion exchange by introducing an alkali component.
According to a fourth aspect of the present invention, in the ultrapure water producing apparatus of the first aspect, the oxidant decomposition unit includes a system for bringing the sampled pure water already undergone ion exchange into contact with platinum or activated carbon.
A fifth aspect of the present invention, an ultrapure water producing apparatus includes: at least two ion exchangers provided in series; a main route provided to flow pure water in the order that the at least two ion exchangers are provided; and a plurality of bypass routes connected to the main route for flowing pure water in the order different from that in which the at least two ion exchangers are provided.
According to a sixth aspect of the present invention, in the ultrapure water producing apparatus of the fifth aspect, the at least two ion exchangers at least include: a first ion exchanger provided on the uppermost stream side; and a second ion exchanger other than the first ion exchanger, discharging first processed pure water, the plurality of bypass routes include a first bypass route, a second bypass route and a third bypass route, the first bypass route supplying the first processed pure water to the at least two ion exchangers except the second ion exchanger discharging the first processed pure water, the second bypass route sending, to the main route, second processed pure water discharged from the at least two ion exchangers except the second ion exchanger which have been supplied with the first processed pure water, and the third bypass route supplying pure water to each of the at least two ion exchangers except the first ion exchanger.
According to a seventh aspect of the present invention, the ultrapure water producing apparatus of the sixth aspect further comprises: an ultrafiltration film provided downstream of the at least two ion exchangers; a fourth bypass route for supplying permeate pure water discharged from the ultrafiltration film to the at least two ion exchangers; and a metal concentration meter for detecting a metal component of the permeate pure water flowing through the fourth bypass route.
According to an eighth aspect of the present invention, in the ultrapure water producing apparatus of the sixth aspect, the main route includes a plurality of main route valves provided on its route for interrupting supply of pure water to the at least two ion exchangers by each one of the at least two ion exchangers, and the plurality of main route valves are closed when flowing pure water through the first to third bypass routes.
A ninth aspect of the present invention is directed to an ultrapure water producing apparatus. The ultrapure water producing apparatus comprises a total organic carbon meter for decomposing an organic substance by applying ultraviolet light to pure water, thereby measuring an organic substance concentration of generated carbon dioxide, wherein the total organic carbon meter includes an oxygen dissolution unit provided on an inlet side of pure water for dissolving oxygen in pure water supplied to the total organic carbon meter.
According to a tenth aspect of the present invention, in the ultrapure water producing apparatus of the ninth aspect, the oxygen dissolution unit includes a system for bubbling, in pure water, oxygen gas or ozone gas not including an organic substance.
According to an eleventh aspect of the present invention, in the ultrapure water producing apparatus of the ninth aspect, the oxygen dissolution unit includes a system for cooling pure water supplied to the total organic carbon meter, thereby supplying cooled pure water with oxygen gas or ozone gas not including an organic substance.
A twelfth aspect of the present invention is directed to an ultrapure water producing apparatus comprising a carbon dioxide dissolution unit provided between an outlet of pure water already undergone final processing and a use point to which pure water is finally supplied, for dissolving carbon dioxide in the pure water already undergone final processing.
According to a thirteenth aspect of the present invention, in the ultrapure water producing apparatus of the twelfth aspect, the carbon dioxide dissolution unit includes a system for bubbling carbon dioxide gas in pure water.
According to a fourteenth aspect of the present invention, in the ultrapure water producing apparatus of the twelfth aspect, the carbon dioxide dissolution unit and the use point are connected by a conductive piping.
In the ultrapure water producing apparatus according to the first aspect, the third dissolved oxygen concentration is a value reflecting the amount of oxidants remaining in the pure water already undergone ion exchange. The use of the remaining amount of oxidants as an index for adjusting the amount of ultraviolet light of the ultraviolet oxidation unit allows more appropriate impurity control compared to a conventional apparatus having no other way but to take only total organic carbon concentration or dissolved oxygen concentration as an index.
In the ultrapure water producing apparatus according to the second aspect, there can be obtained a specific structure of the feedback system for adjusting the amount of ultraviolet light of the ultraviolet oxidation unit.
In the ultrapure water producing apparatus according to the third aspect, the pure water already undergone ion exchange is alkalized to thereby decompose oxidants, which allows the oxidant decomposition unit to have a simple structure.
In the ultrapure water producing apparatus according to the fourth aspect, oxidants are decomposed by the catalytic effect of platinum or activated carbon, which allows the oxidant decomposition unit to have a low running cost.
The ultrapure water producing apparatus according to the fifth aspect comprises at least two ion exchangers provided in series and a plurality of bypass routes for flowing pure water in the order different from that in which the at least two ion exchangers are provided, so that the ion exchangers are replaced one by one. During the period in which a brand-new ion exchanger elutes a metal component, its discharge is given to the remainder of the ion exchangers to remove the metal component, which can prevent pure water including the metal component eluted from the brand-new ion exchanger from being supplied to the use point.
In the ultrapure water producing apparatus according to the sixth aspect, except when one of the ion exchangers provided on the uppermost stream side is replaced, pure water is first supplied to a brand-new ion exchanger through the third bypass route. During the period in which the brand-new ion exchanger elutes a metal component, its discharge is given to the remainder of the ion exchangers to remove the metal component and send it to the main route through the second bypass route, thereby preventing pure water including the metal component eluted from the brand-new ion exchanger from being supplied to the use point.
In the ultrapure water producing apparatus according to the seventh aspect, after replacing an ultrafiltration film, removal of a metal component by supplying the permeate pure water to the at least two ion exchangers through the fourth bypass route is continued until the metal component eluted from the ultrafiltration film reaches a predetermined concentration, which prevents pure water including the metal component eluted from a brand-new ultrafiltration film from being supplied to the use point.
The ultrapure water producing apparatus according to the eighth aspect achieves a specific structure in which it is only after supply of pure water to a brand-new ion exchanger that the remainder of the ion exchangers can be supplied with pure water.
In the ultrapure water producing apparatus according to the ninth aspect, since the total organic carbon meter includes an oxygen dissolution unit for dissolving oxygen in pure water to be measured, an organic substance can be completely decomposed even when there is little oxygen dissolved in pure water, allowing an accurate calculation of organic carbon concentration.
The ultrapure water producing apparatus according to the tenth aspect allows the oxidant decomposition unit to have a relatively simple structure.
The ultrapure water producing apparatus according to the eleventh aspect comprises the system for cooling pure water, which makes it possible to bring pure water into the state in which oxygen gas or ozone gas has an increased solubility. Thus, oxygen gas or ozone gas can be dissolved effectively.
The ultrapure water producing apparatus according to the twelfth aspect comprises the carbon dioxide dissolution unit for dissolving carbon dioxide in pure water already undergone final processing. This can reduce the specific resistance of pure water and make its electrical conductivity good, thereby preventing the piping to the use point from being charged. As a result, this prevents electrically charged particulates from being electrostatically adsorbed on the piping and gathering to form a particle, and prevents sudden desorption of this particle due to variations in pressure or variations in the amount of flow. Therefore, it is possible to reduce particles in pure water.
The ultrapure water producing apparatus according to the thirteenth aspect allows the carbon dioxide dissolution unit to have a relatively simple structure.
In the ultrapure water producing apparatus according to the fourteenth aspect, the carbon dioxide dissolution unit and the use point are connected by the conductive piping, which allows to more effectively prevent the piping from being charged.
An object of the present invention is to provide an ultrapure water producing apparatus with reduced problems resulting from impurities generated after the replacement of unit apparatuses.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.